In telecommunications, asynchronous communication is transmission of data, generally without the use of an external clock signal, where data can be transmitted intermittently rather than in a steady stream. Any timing required to recover data from the communication symbols is encoded within the symbols.
In computer networking, Point-to-Point Protocol (PPP) is a data link layer communication protocol between two routers directly without any host or any other networking in between. It can provide loop connection authentication, transmission encryption, and data compression.
Network throughput refers to the rate of message delivery over a communication channel, such as Ethernet or packet radio, in a communication network. The data that these messages contain may be delivered over physical or logical links, or through network nodes. Throughput is usually measured in bits per second, and sometimes in data packets per second or data packets per time slot.
A frame is a digital data transmission unit in computer networking and telecommunication. In packet switched systems, a frame is a simple container for a single network packet. In other telecommunications systems, a frame is a repeating structure supporting time-division multiplexing.
In computer networking, the transport layer is a conceptual division of methods in the layered architecture of protocols in the network stack in the Internet protocol suite and the OSI model. The protocols of this layer provide end-to-end communication services for applications. It provides services such as connection-oriented communication, reliability, flow control, and multiplexing.
In telecommunications and computing, bit rate is the number of bits that are conveyed or processed per unit of time.
AX.25 is a data link layer protocol originally derived from layer 2 of the X.25 protocol suite and designed for use by amateur radio operators. It is used extensively on amateur packet radio networks.
Throughput of a network can be measured using various tools available on different platforms. This page explains the theory behind what these tools set out to measure and the issues regarding these measurements.
ZMODEM is an inline file transfer protocol developed by Chuck Forsberg in 1986, in a project funded by Telenet in order to improve file transfers on their X.25 network. In addition to dramatically improved performance compared to older protocols, ZMODEM offered restartable transfers, auto-start by the sender, an expanded 32-bit CRC, and control character quoting supporting 8-bit clean transfers, allowing it to be used on networks that would not pass control characters.
XMODEM is a simple file transfer protocol developed as a quick hack by Ward Christensen for use in his 1977 MODEM.ASM terminal program. It allowed users to transmit files between their computers when both sides used MODEM. Keith Petersen made a minor update to always turn on "quiet mode", and called the result XMODEM.
YMODEM is a file transfer protocol used between microcomputers connected together using modems. It was primarily used to transfer files to and from bulletin board systems. YMODEM was developed by Chuck Forsberg as an expansion of XMODEM and was first implemented in his CP/M YAM program. Initially also known as YAM, it was formally given the name "YMODEM" in 1985 by Ward Christensen, author of the original XMODEM.
Protocol spoofing is used in data communications to improve performance in situations where an existing protocol is inadequate, for example due to long delays or high error rates.
SEAlink is a file transfer protocol that is backward compatible with XMODEM but features a sliding window system for improved throughput. SEAlink was written in 1986 as a part of the SEAdog FidoNet mailer written by System Enhancement Associates, creators of the famous ARC program. It was licensed with a simple "give credit" requirement, but nevertheless was not very widely used except in FidoNet mailers. SEAlink, and most other XMODEM enhancements, were quickly displaced following the introduction of ZMODEM.
C-Modem is a protocol driver developed by Lavio Pareschi in 1989, that works similarly and better than ZMODEM. It includes a whole new file transfer protocol, built around the idea of crash recovery, easy of use and great performance. C-Modem provides reliable file transmission even in the worst conditions, as it adapts itself immediately to any errors that may occur.
ZMax is a file transfer protocol developed in 1990-1991 by Mike Bryeans who also developed TMODEM.
The Microcom Networking Protocols, almost always shortened to MNP, is a family of error-correcting protocols commonly used on early high-speed modems. Originally developed for use on Microcom's own family of modems, the protocol was later openly licensed and used by most of the modem industry, notably the "big three", Telebit, USRobotics and Hayes. MNP was later supplanted by v.42bis, which was used almost universally starting with the first v.32bis modems in the early 1990s.
Asymmetric digital subscriber line (ADSL) is a type of digital subscriber line (DSL) technology, a data communications technology that enables faster data transmission over copper telephone lines than a conventional voiceband modem can provide. ADSL differs from the less common symmetric digital subscriber line (SDSL). In ADSL, bandwidth and bit rate are said to be asymmetric, meaning greater toward the customer premises (downstream) than the reverse (upstream). Providers usually market ADSL as an Internet access service primarily for downloading content from the Internet, but not for serving content accessed by others.
Janus is a file transfer protocol for use on bulletin board systems (BBSs). It has the relatively rare feature that it is fully bidirectional, allowing the protocol to upload and download files at the same time. It was written by Rick Huebner in 1987; Huebner had previously written a ZMODEM module for the Opus-CBBS system.
MEGAlink is a file transfer protocol for modem-equipped microcomputers written by Paul Meiners in 1987. Like many protocols of the era, MEGAlink is an expanded version of the seminal XMODEM. While it was a relatively simple and high-performance system, it remains relatively obscure because it was overshadowed by ZMODEM, which had been released a year earlier and saw rapid uptake.
